This invention is related to the field of semiconductor devices. More specifically, the invention is a leadout for diffused circuit elements in semiconductor devices which reduces surface effects and parasitic resistance and a method of making the leadout.
Semiconductor devices have defined paths of low resistivity which can be used as interconnections to external circuitry. Generally, the leadout is created by highly doping a region of the device by diffusing extra donors or acceptors into a portion of the semiconductor device. However, this diffusion must have a long tail with a small grading coefficient so that breakdown with a protective overlayer can be avoided. To avoid breakdown, a deep diffusion is required. A deep diffusion requires long diffusion times and the depth of the diffusion is limited by the depth of the device. Because of the time required and a maximum depth constraint, there is a minimum sheet resistance which is obtainable. It is desirable to have a lower sheet resistance leadout to reduce the drift caused by electrical surface effects over the contacting material and to reduce parasitic resistance.